problem accessing phone storage

i have a galaxy s4 mini and i used to be able to access the files on the storage (internal and sd card) by plugging in the usb cable. Now the phone wont go into usb mode and i dont know why. The pc is fine and the cables are fine...its the phone. I tried this on two different pcs and nothing works and they are both pcs that I use often...one at work and one at home my phone is not rooted

Hello. Some suggestions.
If you set a secure screen lock it won't access, swipe only. Try downloading Samsung Kies for new drivers, if you don't have it. When you connect to the pc usb port you should get a notification saying connected as a MTP or PTP device, pull down to change.
Cable may be faulty in one direction, but charges OK.